1. Field of the Invention
This invention generally relates to a recording disk drive motor, in particular to a thin and small type recording disk drive motor rotatably driving a removable type recording disk such as a CD-ROM, a DVD or the like, and a recording disk drive employing the motor, a method of manufacturing a stator used in the recording disk drive motor, and core plate that is used in the manufacture of the stator.
2. Background Art
In recent years, disk drives that use a motor to rotatively drive a removable type recording disk such as a CD-ROM, a DVD or the like have begun to be used in mobile devices, e.g., devices such as digital cameras and personal digital assistants (PDAs). In such devices, small size and portability are very important features, therefore, there is a need for the diameter of the recording disk to be reduced when this type of disk drive is used in these types of mobile devices. Naturally, the disk drive and the disk drive motor employed therein is expected to become smaller and thinner as well.
It is known that axial gap type recording disk driving motors can be used to reduce the diameter of the motor. However, the axial gap type motor is difficult to use in the thin type recording disk drive because the axial gap type motor includes a rotor magnet and a stator disposed to axially oppose each other across an axial gap.
On the other hand, radial gap type motors can reduce the axial height of the motor, however, there must be a special ingenious device for reducing the diameter of radial gap type motors because the radial gap type motor include a rotor magnet and a stator disposed to radially oppose each other across a radial gap. Thus, if the diameter of an outer rotor type motor (in which the rotor magnet is disposed on the outer circumferential side of the stator) is reduced by reducing the quantity of the coil wound around the stator, then rotational torque generated by interaction of the magnetic fields of the stator and the rotor magnet will be reduced. It is therefore difficult to reduce the diameter of the outer rotor type motor. However, an inner rotor type motor (in which the rotor magnet is disposed on the inner circumferential side of the stator) can be used as a radial gap type motor in a thin and small type recording disk drive, because the inner rotor type motor can maintain the quantity of the coil wound around the stator by using vacant space in the disk drive, and thus the torque generated by the stator and the rotor magnet is not reduced even if the diameter of the rotor is reduced. The stator of the inner rotor type motor includes a stator core that has an annular core back and a plurality of stator teeth that extend inward in the radial direction from an inner circumferential surface defining the circular hole, and windings that are wound around each of the stator teeth. Each of the stator teeth and the windings form a plurality of stator poles, and the stator core is mounted on a base member of the motor or the disk drive. The stator core is formed from a plurality of core plates laminated therewith and fixed together by means of caulking or laser welding. The rotor of the inner rotor type motor includes a rotor magnet that faces the stator poles and disposed inside of the annular core back in the radial direction, and a recording disk mounting portion for mounting the recording disk.
As described above, the diameter of the rotor in the inner rotor type motor can be reduced to some extent. It is, however, difficult to avoid interference with the operation of the read/write head and/or other parts in the disk drive and maintain enough rotational speed and torque in the disk drive motor.
In addition, reducing the axial height or span of a bearing employed in the motor of a disk drive will make the motor and the disk driver thinner. The bearing functions to center-balance the rotor in the radial direction, and prevent vibration or wobble in the rotor. The effectiveness of the bearing in maintaining the rotor in a constant concentric rotational relationship with the rotational axis of the motor depends on the rigidity of the bearing and the axial height or span of the bearing. However, the rotational precision of the motor will worsen as the axial height or span of the bearing is reduced, therefore reducing the axial height of the motor presents difficulties.
Furthermore, the width of the core back of the stator (the length thereof in the radial direction) may be reduced, and as a result the magnetic path of the magnetic circuit or the fixing portion for caulking or laser welding may be insufficient.
The above described problems become serious when a removable recording disk having a diameter of 30 mm or less is used. In fact, in accordance with minimization of the size of mobile devices, a recording disk having a diameter of 30 mm or less is being considered for use in such devices.
In addition, the stator is normally manufactured as follows. First, a magnetic steel sheet (e.g., a silicon steel sheet) is cut by any one of a variety of press works, thereby obtaining a core plate having a desired shape including a plurality of stator teeth (the forming process). Next, a stator core is formed by stacking a number of the core plates on top of one another (the lamination process), and then caulking them together (the fixing process). After this step, an insulating material is coated onto the surface of the stator core by spraying or evaporation (the insulating process). Finally, a wire is wound 20 times around each stator tooth of the insulated stator core while the stator core is chucked by chucking unit of a coil winding apparatus (the winding process), thereby forming a stator having windings wound around the stator teeth.
However, in accordance with the overall reduction in the diameter and thickness of motors, the diameter and the thickness of stator cores also continue to decrease, and thus the stiffness of the stator core is reduced. As a result, the stator core may be deflected when it is chucked by a coil winding apparatus.